Interpretive Summary: Pine straw is a valuable landscaping mulch and harvesting it has become a multi-million dollar business in several southeastern states, but some forest managers are concerned that the loss of this soil cover from the forest may increase drought stress on the trees in areas where pine straw has been harvested. To address such concerns, research was conducted to determine the effect of pine straw harvesting on soil moisture levels in a loblolly pine forest during the dry season. This study showed that pine straw harvesting decreased water content in the pine root zone during part of the dry season in the first year after the pine straw was removed. The study is of interest to scientists, foresters, extension personnel, and producers because it provides evidence that pine straw harvesting can potentially increase drought stress on loblolly pine unless management practices are developed to quickly replace the forest soil cover after a pine straw harvest occurs.

Technical Abstract:
Pine needles that accumulate on the forest floor help to conserve soil moisture, protect the soil surface against erosion, moderate soil temperature, inhibit weed growth, and provide soil nutrients and organic matter. These qualities make pine straw a valuable landscaping mulch that has become a multi-million dollar business in several southeastern states. However, some forest managers are concerned that the loss of those mulching benefits from forests may decrease timber productivity in areas where pine straw has been harvested. The primary concern is that removal of the protective pine straw layer allows water to evaporate more quickly from the soil surface. Therefore, we hypothesized that pine straw harvesting decreases water content of the soil vadose zone, which could potentially increase drought stress on the trees. To test this hypothesis, three pine-straw harvesting practices (schedules) and a control treatment (no straw harvest) were compared to determine harvesting effects on water content of the soil vadose zone in an established (16 yrs) loblolly (Pinus taeda L.) plantation (3.0 x 1.5 m tree spacing). There were 24 plots (0.18 ha each) to provide six replications of each harvesting treatment. Volumetric soil water content (%) was measured by time domain reflectometry (TDR) for 25 weeks (June to November) at 20-, 50-, and 80-cm depths. Results showed that pine straw harvesting tended to decrease soil water content at depths below 20 cm, but the effect was significant (P<0.05) only at the 50-cm depth in weeks 3 and 4 (late June) of the study, when water content at this depth averaged 20.9% for soils where straw was harvested annually, and 30.2% for soils where the straw was never harvested (control). In soils where pine straw had been allowed to accumulate for at least a year after being harvested, average water content was not significantly different than in the control plots. Therefore, pine straw harvesting can potentially lengthen drought-stress periods for loblolly pine during the first year after pine straw has been removed.